Differential Survival in Common Grackles Sprayed with Turgitol

Abstract

Collections of male common grackles Quiscalus quiscula made following application of the wetting agent Turgitol and water showed differential survival of phenotypes. Analysis of polymorphic enzymes showed no differences between survivors and nonsurvivors. Heterozygosity was generally low. Principal-component analysis of mensural characters showed selection in favor of smaller, less stocky individuals. This pattern is opposite to that found by Bumpus''s (1899) analysis of the house sparrow. Two possible interpretations are discussed: sexual selection for larger males results in features that are not adaptive for survival outside the breeding season, and larger males roost higher in the trees and are exposed to a heavier application of Turgitol and water.